Lower limb exoskeleton system having jump-down cushioning function and use method thereof

ABSTRACT

A lower limb exoskeleton system includes a back frame, hip joint movement mechanisms, telescopic thigh bars, knee joint movement mechanisms, shank bars, foot jump-down cushioning mechanisms, a waist binding frame, upper leg binding frames and lower leg binding frames. Two protruding ends of the back frame are connected with one end of each of the telescopic thigh bars respectively via the hip joint movement mechanisms, the other ends of the telescopic thigh bars are connected with one end of the corresponding shank bars respectively via the knee joint movement mechanisms, and the other ends of the shank bars are connected with the foot jump-down cushioning mechanisms. The waist binding frame is arranged on an inner side of a horizontal part of the back frame, and the upper leg binding frames and the lower leg binding frames are arranged on the telescopic thigh bars and the shank bars respectively.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention belongs to the technical field of mechatronic engineering and biomedical engineering, and more particularly, to provide a lower limb exoskeleton system having jump-down cushioning function and a use method thereof.

2. The Prior Arts

Lower limb exoskeleton is a wearable machine made of a metal frame, and can enhance the lower limb function of human bodies. In the military field, the lower limb exoskeleton can drive mechanical joints to perform actions according to physical acts of human, and help a wearer to run faster and be high in loading capacity. In the medical rehabilitation field, the lower limb exoskeleton can assist in recovering the leg walking ability of the elderly and the disabled people wearing the lower limb exoskeleton, and even help paralyzed people to stand and walk again.

At current, most of lower limb exoskeletons are used for assisting in the wearer to walk and run on flat ground and go upstairs. When the wearer jumps down, the lower limb exoskeletons are needed to have the cushioning function for resisting ground reaction force. However, most of current lower limb exoskeletons neither have such function, nor ensure the lower limb safety of the wearer when the wearer jumps down from a high place. For this reason, the application proposes a lower limb exoskeleton system having jump-down cushioning function, i.e. the lower limb exoskeleton system provides the cushioning function for resisting ground reaction force based on an instruction given by the wearer when the wearer jumps down, so that the lower limb exoskeleton system can protect the lower limbs from being damaged when the wearer jumps down. The lower limb exoskeleton system has foot jump-down cushioning mechanisms at the points of the lower limb exoskeleton system with ground, which meet the cushioning requirements of 1.5 m jump-down height.

SUMMARY OF THE INVENTION

A primary objective of the present invention is to provide a lower limb exoskeleton system having jump-down cushioning function and a use method thereof.

For achieving the foregoing objectives, the present invention provides a lower limb exoskeleton system having jump-down cushioning function. The lower limb exoskeleton system having jump-down cushioning function comprises a back frame, hip joint movement mechanisms, telescopic thigh bars, knee joint movement mechanisms, shank bars, foot jump-down cushioning mechanisms, a waist binding frame, upper leg binding frames and lower leg binding frames; wherein two protruding ends of the back frame are connected with one end of each of the telescopic thigh bars respectively via the hip joint movement mechanisms, the other ends of the telescopic thigh bars are connected with one end of the corresponding shank bars respectively via the knee joint movement mechanisms, and the other ends of the shank bars are connected with the foot jump-down cushioning mechanisms; and the waist binding frame is arranged on an inner side of a horizontal part of the back frame, and the upper leg binding frames and the lower leg binding frames are arranged on the telescopic thigh bars and the shank bars respectively.

Each of the hip joint movement mechanisms consists of an abduction and adduction moving piece, a flexion and extension moving piece and an upper thigh bar connecting frame, wherein one end of the abduction and adduction moving piece is connected with the back frame through bolts, and the other end of the abduction and adduction moving piece is connected with one end of the flexion and extension moving piece via a first pin; the other end of the flexion and extension moving piece is connected with one end of the upper thigh bar connecting frame via a second pin; and the first pin and the second pin are perpendicular to each other.

Each of the telescopic thigh bars consists of an upper thigh bar and a lower thigh bar, wherein three rows of threaded through holes are formed on an upper end of the lower thigh bar in one row, and the upper end of the lower thigh bar is connected with a bottom end of the upper thigh bar via the threaded through holes and bolts; a top end of the upper thigh bar is threadedly connected with an upper thigh bar connecting frame of the hip joint movement mechanism, and the upper leg binding frame is connected to an outer circular surface of the upper thigh bar through bolts; and two through holes are formed on an ear plate at a bottom end of the lower thigh bar in one row.

Each of the knee joint movement mechanisms consists of two lower thigh bar connecting frames, a knee joint rotating piece, a harmonic reducer and a motor, wherein the two lower thigh bar connecting frames are connected with a bottom end of a lower thigh bar of the telescopic thigh bar through bolts, and one of the lower thigh bar connecting frames is connected with a flexible gear of the harmonic reducer and the motor respectively; the harmonic reducer is located on an inner side of one of the lower thigh bar connecting frames, the motor is located on an outer side of one of the lower thigh bar connecting frames, a harmonic generator of the harmonic reducer is connected with an output shaft of the motor, and a steel output gear of the harmonic reducer is connected with the knee joint rotating piece located between the two lower thigh bar connecting frames; a bottom end of the knee joint rotating piece is connected with a top end of the shank bar through bolts, and fixed-angle notch bosses are arranged on connecting sides of the two lower thigh bar connecting frames with the knee joint rotating piece.

Each of the foot jump-down cushioning mechanisms consists of an electromagnet, an electromagnet fixing frame, traction ropes, clamps, a rubber mat, a shell, a moving sleeve, a cushioning spring, reset springs and a control module, wherein top of the shell is connected with a bottom end of the shank bar through bolts, the moving sleeve is arranged in an inner side of the shell, the cushioning spring is arranged in the moving sleeve, top of the cushioning spring is abutted to an inner limiting plate in the shell, the clamps are symmetrically arranged on an outer circular surface of a lower middle part of the shell, middle parts of the clamps are hinged with the shell, and the reset springs are arranged between circular surfaces at one ends of the clamps and bosses of the shell; tail ends with circular surfaces of the clamps are connected with one ends of the traction ropes, and the other ends of the traction ropes are connected with the electromagnet; the electromagnet is arranged on the electromagnet fixing frame through bolts, and the electromagnet fixing frame is fixed to the shank bar through bolts; the other ends of the clamps are connected with a bottom end of the moving sleeve, the bottom end of the moving sleeve is connected with the rubber mat through bolts, Bonding surfaces between the rubber mat and the moving sleeve are bound through rubber-metal adhesive glue, and grooves are symmetrically formed on two ends of the rubber mat; and the control module is connected with the electromagnet.

The control module comprises an upper computer, a wireless communication module, a control panel and a relay, wherein the upper computer is connected with the control panel through the wireless communication module, the control panel is electrically connected with the relay, and the relay is electrically connected with the electromagnet.

For achieving the foregoing objectives, the present invention provides a use method of the lower limb exoskeleton system having jump-down cushioning function. The use method of the lower limb exoskeleton system having jump-down cushioning function comprises the following steps:

step 1: the lower limb exoskeleton system is worn to a lower half part of a human body of a wearer, the back frame of the lower limb exoskeleton system is fixed to a waist of the wearer through binding tapes and the waist binding frame, the telescopic thigh bars are fixed to thighs of the wearer through the upper leg binding frames and binding tapes, and the shank bars are fixed to shanks of the wearer through the lower leg binding frames and binding tapes; and

step 2: when the wearer walks on flat ground, motors in the knee joint movement mechanisms output torque to control the walking action, and harmonic reducers of the knee joint movement mechanisms convert rotation of outer shafts of the motors into flexion and extension movements of the knee joint movement mechanisms, so that the hip joint movement mechanisms are driven to passively follow the wearer to move; when jump-down movement is needed, the upper computer sends instructions to the control panel via the wireless communication module, output pins of the control panel control the relay to be connected, the electromagnet is electrified to be connected to drag the traction ropes and open the clamps, and the cushioning spring compressed into the shell pushes the moving sleeve to a limit position under the action of spring force; in a landing process, the rubber mat is in contact with the ground and presses the moving sleeve into the shell under the action of ground support forces, so that the cushioning spring is compressed into the shell again; after complete landing, the upper computer sends instructions to control the control panel, and the output pins of the control panel control the relay to be disconnected so as to disconnect the electromagnet and loosen the traction ropes; and the clamps are pushed to clamp the moving sleeve under the action of the reset springs, and therefore, the cushioning spring is compressed in the shell without popping out to finish an entire jump-down cushioning action.

The lower limb exoskeleton system has the beneficial effects that:

First of all, the application proposes a lower limb exoskeleton system having jump-down cushioning function, i.e. the lower limb exoskeleton system provides the cushioning function for resisting ground reaction force based on an instruction given by the wearer while jumping down, so that the lower limb exoskeleton system can protect the lower limbs from being damaged when the wearer jumps down.

Secondly, the lower limb exoskeleton system has foot jump-down cushioning mechanisms at the points of contact with ground. Based on the energy conservation principle, the change in gravitational potential energy equals to the energy absorbed by the human body and the lower limb exoskeleton system through cushioning. Because energy absorbed by the human body through cushioning is limited, protection to the human body should be increased, i.e. energy to be absorbed by the human body in the cushioning process needs to be reduced. When cushioning springs of the foot jump-down cushioning mechanisms are compressed in the landing process, one part of gravitational potential energy is converted into internal energy of the cushioning springs, and the energy absorption ability of the lower limb exoskeleton system is improved, so that the energy absorbed by the human body is reduced, the safety of the human body in jump-down landing is guaranteed, and the cushioning need of 1.5 m jump-down height is satisfied.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front overall structural diagram of a lower limb exoskeleton system of the present invention;

FIG. 2 is a front structural diagram of a hip joint movement mechanism of the lower limb exoskeleton system of the present invention;

FIG. 3 is a front structural diagram of a telescopic thigh bar of the lower limb exoskeleton system of the present invention;

FIG. 4 is a structural diagram of a knee joint movement mechanism of the lower limb exoskeleton system of the present invention;

FIG. 5 is a structural diagram of a foot jump-down cushioning mechanism of the lower limb exoskeleton system of the present invention;

FIG. 6 is a part control flow chart of the foot jump-down cushioning mechanism of the lower limb exoskeleton system of the present invention; and

FIG. 7 is a diagram for virtual wearing of the lower limb exoskeleton system of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is further described hereinafter in combination with accompanying drawings and embodiments.

As shown in FIGS. 1-7, a lower limb exoskeleton system having jump-down cushioning function comprises a back frame 1, hip joint movement mechanisms 2, telescopic thigh bars 7, knee joint movement mechanisms 4, shank bars 8, foot jump-down cushioning mechanisms 5, a waist binding frame 6, upper leg binding frames 3 and lower leg binding frames 17. Two protruding ends of the back frame 1 are connected with one end of each of the telescopic thigh bars 7 respectively via the hip joint movement mechanisms 2, the other ends of the telescopic thigh bars 7 are connected with one end of the corresponding shank bars 8 respectively via the knee joint movement mechanisms 4, and the other ends of the shank bars 8 are threadedly connected with the foot jump-down cushioning mechanisms 5. The waist binding frame 6 is arranged on an inner side of a horizontal part of the back frame 1, and the upper leg binding frames 3 and the lower leg binding frames 17 are arranged on the telescopic thigh bars 7 and the shank bars 8 respectively.

Each of the hip joint movement mechanisms 2 consists of an abduction and adduction moving piece 9, a flexion and extension moving piece 10 and an upper thigh bar connecting frame 11. One end of the abduction and adduction moving piece 9 is connected with the back frame 1 through bolts, and the other end of the abduction and adduction moving piece 9 is connected with one end of the flexion and extension moving piece 10 via a first pin to realize the abduction and adduction movements of the lower limb exoskeleton system. The other end of the flexion and extension moving piece 10 is connected with one end of the upper thigh bar connecting frame 11 via a second pin to form a rotating pair to realize flexion and extension movements of the hip joint movement mechanism 2. The first pin and the second pin are perpendicular to each other. The hip joint movement mechanism 2 of the present invention has two degrees of freedom.

Each of the telescopic thigh bars 7 consists of an upper thigh bar 12 and a lower thigh bar 13. The upper thigh bar 12 and the lower thigh bar 13 are both made of aluminum tubes, three rows of threaded through holes are formed on an upper end of the lower thigh bar 13 in one row, and the upper end of the lower thigh bar 13 is connected with a bottom end of the upper thigh bar 12 via the threaded through holes and bolts to realize the stepped length adjustment of the telescopic thigh bar 7. A top end of the upper thigh bar 12 is threadedly connected with the upper thigh bar connecting frame 11, and the upper leg binding frame 3 is connected to a middle part of an outer circular surface of the upper thigh bar 12 through bolts. Two through holes are formed on an ear plate at a bottom end of the lower thigh bar 13 in one row.

Each of the knee joint movement mechanisms 4 consists of two lower thigh bar connecting frames 14, a knee joint rotating piece 15, a harmonic reducer 16 and a motor 18. The two lower thigh bar connecting frames 14 are connected with the bottom end of the lower thigh bar 13 through bolts, and one of the lower thigh bar connecting frames 14 is connected with a flexible gear of the harmonic reducer 16 and the motor 18 respectively. The harmonic reducer 16 is located on an inner side of one of the lower thigh bar connecting frames 14, the motor 18 is located on an outer side of one of the lower thigh bar connecting frames 14, a harmonic generator of the harmonic reducer 16 is connected with an output shaft of the motor 18, and a steel output gear of the harmonic reducer 16 is connected with the knee joint rotating piece 15 located between the two lower thigh bar connecting frames 14. A bottom end of the knee joint rotating piece 15 is connected with a top end of the shank bar 8 through bolts, and fixed-angle notch bosses are arranged on connecting sides of the two lower thigh bar connecting frames 14 with the knee joint rotating piece 15. When the knee joint rotating piece 15 rotates to front and rear limit positions to be connected with the fixed-angle notch bosses on the lower thigh bar connecting frames 14, a limit movement position of the knee joint movement mechanism 4 is limited. An angle sensor is mounted on the motor 18 to prevent the flexion and extension movements of the knee joint movement mechanism 4 from out of normal range. The motor 18 outputs certain torque to drive the lower limb exoskeleton system to assist in the movement of human knee joints according to the movement principles and characteristics of human lower limbs in normal walking.

Each of the foot jump-down cushioning mechanisms 5 consists of an electromagnet 19, an electromagnet fixing frame 20, traction ropes 21, clamps 22, a rubber mat 23, a shell 24, a moving sleeve 25, a cushioning spring 26, reset springs 27 and a control module. Top of the shell 24 is connected with a bottom end of the shank bar 8 through bolts, the moving sleeve 25 is arranged in an inner side of the shell 24, the shell 24 consists of two semicircular shells, protruding flanges are arranged on end surfaces of the semicircular shells, and the two semicircular shells are fixedly mounted through the protruding flanges and the bolts to form the shell 24. The cushioning spring 26 is arranged in the moving sleeve 25, an inner stop block is arranged at a bottom end of an inner wall of the shell 24, an outer stop block is arranged at a top end of an outer wall of the moving sleeve 25, the inner stop block of the shell 24 and the outer stop block of the moving sleeve 25 are in buckling to prevent the moving sleeve 25 from moving out of the shell 24, and top of the cushioning spring 26 is abutted against an inner limiting plate of the shell 24. The clamps 22 are symmetrically arranged on an outer circular surface of a lower middle part of the shell 24, middle parts of the clamps 22 are hinged with the shell 24, and the reset springs 27 are arranged between circular surfaces at upper ends of the clamps 22 and bosses of the shell 24. The reset springs 27 are always in compressed state, and the clamps 22 are pushed by the spring force of the reset springs 27 during jumping down so that lower ends of the clamps 22 tightly press against a lower end surface of the moving sleeve 25. Tail ends with circular surfaces of the clamps 22 are connected with one ends of the traction ropes 21, and the other ends of the traction ropes 21 are connected with the electromagnet 19. The electromagnet 19 is a push-pull frame DC electromagnet and is arranged on the electromagnet fixing frame 20 through bolts, and the electromagnet fixing frame 20 is fixed on the shank bar 8 through bolts. Bending parts at the lower ends of the clamps 22 are connected with a bottom end of the moving sleeve 25 to limit the position of the moving sleeve 25, and the bending parts at the lower ends of the clamps 22 form a 90-degree angle with main body parts of the clamps 22. The bottom end of the moving sleeve 25 is connected with the rubber mat 23 through bolts, and bonding surfaces between the rubber mat 23 and the moving sleeve 25 are bound through rubber-metal adhesive glue. Grooves 28 are symmetrically formed on two ends of the rubber mat 23 so that the clamps 22 have enough movement space in expansion. The control module is connected with the electromagnet 19.

The control module comprises an upper computer, a wireless communication module, a control panel and a relay. The upper computer is connected with the control panel through the wireless communication module, the control panel is electrically connected with the relay, and the relay is electrically connected with the electromagnet 19. The control panel is mainly used for controlling the power-on and power-off of the push-pull frame DC electromagnet 19 to further control the opening and closing of the clamps 22. The upper computer is an ordinary notebook computer, the wireless communication module is ZigBee wireless communication module, the control panel is arduino mega2560 control panel, and the relay is telesky24V relay.

A use method of the lower limb exoskeleton system having jump-down cushioning function comprises the following steps:

Step 1: the lower limb exoskeleton system is worn to a lower half part of a human body of a wearer, the back frame 1 of the lower limb exoskeleton system is fixed to a waist of the wearer through binding tapes and the waist binding frame 6, the telescopic thigh bars 7 are fixed to thighs of the wearer through the upper leg binding frames 3 and binding tapes, and the shank bars 8 are fixed to shanks of the wearer through the lower leg binding frames 17 and binding tapes; and

Step 2: when the wearer walks on flat ground, the motors 18 in the knee joint movement mechanisms 4 output torque to control the walking action, and the harmonic reducers 16 convert rotation of the outer shafts of the motors into flexion and extension movements of the knee joint movement mechanisms 4, so that the hip joint movement mechanisms 2 are driven to passively follow the wearer to move; when down jumping movement is needed, the upper computer sends instructions to the control panel via the wireless communication module, output pins of the control panel control the relay to be connected, the push-pull frame DC electromagnet 19 is electrified to be connected to drag the traction ropes 21 and open the clamps 22, and the cushioning spring 26 compressed in the shell 24 pushes the moving sleeve 25 to a limit position under the action of spring force; in a landing process, the rubber mat 23 is in contact with the ground and presses the moving sleeve 25 into the shell 24 under the action of ground support forces, so that the cushioning spring 26 is compressed into the shell 24 again; after complete landing, the upper computer sends instructions to control the control panel, and the output pins of the control panel control the relay to be disconnected so as to disconnect the push-pull frame DC electromagnet 19 and loosen the traction ropes 21; and the clamps 22 are pushed to clamp the moving sleeve 25 under the action of the reset springs 27, and therefore, the cushioning spring 26 is compressed in the shell 24 without popping out to finish an entire jump-down cushioning action.

Embodiment 1

Ordinary people without special training are usually not liable to damage when jumping down from the height of 1.5 m. When the height is greater, people have a risk of injuries. This critical height is reduced when people are in load state. Therefore, it is assumed that a human wearing the lower limb exoskeleton system jumps down in free fall from 1.5 m height at an initial velocity of 0 m/s and the initial gravitational potential energy is W_(g). Because the lower limb exoskeleton system and the human body system are high in mass, the impact of air resistance in falling is ignored. When the human jumps down to touch the ground, the final velocity is reduced to 0 m/s. During the process when the human and the lower limb exoskeleton system stop movement steadily, the energy absorbed by the cushioning of human skeletal muscles and joints is W₁, and the energy absorbed by the foot jump-down cushioning mechanisms of the lower limb exoskeleton system is W₂. According to the principle of energy conservation, it can be deduced that:

W _(g) =W ₁ +W ₂

which is equivalent to:

W ₁ =W _(g) −W ₂

Because the skeletal muscle and joint system of the human body has own utmost carrying ability, i.e. the skeletal muscle and joint system has limited cushioning ability, the energy absorbed by the skeletal muscle and joint system in the cushioning process is limited and set as W_(1max). W₁=W_(1max) needs to be satisfied so as to ensure the safety of human body in jumping down, that is W₁ needs to be reduced. For each jump, other energy losses are not considered for the human body and the lower limb exoskeleton system during the entire jumping down process, and the initial gravitational potential energy W_(g) is constant. Thus, W₁ can be reduced by increasing the cushioning ability of the lower limb exoskeleton system, i.e. W₂. In this embodiment, an elastic energy absorbing element in the foot jump-down cushioning mechanisms are springs. The stiffness factor of the springs is set as K, the compression displacement of the springs in one-time jumping down process is A, the energy absorbed by the springs in one-time jumping down process is W_(spring)=½KΔx², the impact of other parts of the lower limb exoskeleton system to energy is ignored, both feet have foot jump-down cushioning mechanisms, and therefore, it can be deduced that:

W ₂=2W _(spring) =KΔx ²

the two formulas are combined to obtain that:

W ₁ =W _(g) −KΔx ²

It can be known that the cushioning ability of the lower limb exoskeleton system can be adjusted by adjusting the stiffness of the springs in the foot jump-down cushioning mechanisms to meet different use requirements, so that the human body can be cushioned and protected when the wearer jumps down. 

What is claimed is:
 1. A lower limb exoskeleton system having jump-down cushioning function, comprising: a back frame, hip joint movement mechanisms, telescopic thigh bars, knee joint movement mechanisms, shank bars, foot jump-down cushioning mechanisms, a waist binding frame, upper leg binding frames and lower leg binding frames; wherein two protruding ends of the back frame are connected with one end of each of the telescopic thigh bars respectively via the hip joint movement mechanisms, the other ends of the telescopic thigh bars are connected with one end of the corresponding shank bars respectively via the knee joint movement mechanisms, and the other ends of the shank bars are connected with the foot jump-down cushioning mechanisms; and the waist binding frame is arranged on an inner side of a horizontal part of the back frame, and the upper leg binding frames and the lower leg binding frames are arranged on the telescopic thigh bars and the shank bars respectively; and wherein each of the foot jump-down cushioning mechanisms consists of an electromagnet, an electromagnet fixing frame, traction ropes, clamps, a rubber mat, a shell, a moving sleeve, a cushioning spring, reset springs and a control module, wherein top of the shell is connected with a bottom end of the shank bar through bolts, the moving sleeve is arranged in an inner side of the shell, the cushioning spring is arranged in the moving sleeve, top of the cushioning spring is abutted to an inner limiting plate in the shell, the clamps are symmetrically arranged on an outer circular surface of a lower middle part of the shell, middle parts of the clamps are hinged with the shell, and the reset springs are arranged between circular surfaces at one ends of the clamps and bosses of the shell; tail ends with circular surfaces of the clamps are connected with one ends of the traction ropes, and the other ends of the traction ropes are connected with the electromagnet; the electromagnet is arranged on the electromagnet fixing frame through bolts, and the electromagnet fixing frame is fixed to the shank bar through bolts; the other ends of the clamps are connected with a bottom end of the moving sleeve, the bottom end of the moving sleeve is connected with the rubber mat through bolts, bonding surfaces between the rubber mat and the moving sleeve are bound through rubber-metal adhesive glue, and grooves are symmetrically formed on two ends of the rubber mat; and the control module is connected with the electromagnet.
 2. The lower limb exoskeleton system according to claim 1, wherein each of the hip joint movement mechanisms consists of an abduction and adduction moving piece, a flexion and extension moving piece and an upper thigh bar connecting frame, wherein one end of the abduction and adduction moving piece is connected with the back frame through bolts, and the other end of the abduction and adduction moving piece is connected with one end of the flexion and extension moving piece via a first pin; the other end of the flexion and extension moving piece is connected with one end of the upper thigh bar connecting frame via a second pin; and the first pin and the second pin are perpendicular to each other.
 3. The lower limb exoskeleton system according to claim 1, wherein each of the telescopic thigh bars consists of an upper thigh bar and a lower thigh bar, wherein three rows of threaded through holes are formed on an upper end of the lower thigh bar in one row, and the upper end of the lower thigh bar is connected with a bottom end of the upper thigh bar via the threaded through holes and bolts; a top end of the upper thigh bar is threadedly connected with an upper thigh bar connecting frame of the hip joint movement mechanism, and the upper leg binding frame is connected to an outer circular surface of the upper thigh bar through bolts; and two through holes are formed on an ear plate at a bottom end of the lower thigh bar in one row.
 4. The lower limb exoskeleton system according to claim 1, wherein each of the knee joint movement mechanisms consists of two lower thigh bar connecting frames, a knee joint rotating piece, a harmonic reducer and a motor, wherein the two lower thigh bar connecting frames are connected with a bottom end of a lower thigh bar of the telescopic thigh bar through bolts, and one of the lower thigh bar connecting frames is connected with a flexible gear of the harmonic reducer and the motor respectively; the harmonic reducer is located on an inner side of one of the lower thigh bar connecting frames, the motor is located on an outer side of one of the lower thigh bar connecting frames, a harmonic generator of the harmonic reducer is connected with an output shaft of the motor, and a steel output gear of the harmonic reducer is connected with the knee joint rotating piece located between the two lower thigh bar connecting frames; a bottom end of the knee joint rotating piece is connected with a top end of the shank bar through bolts, and fixed-angle notch bosses are arranged on connecting sides of the two lower thigh bar connecting frames with the knee joint rotating piece.
 5. The lower limb exoskeleton system according to claim 1, wherein the control module comprises an upper computer, a wireless communication module, a control panel and a relay, wherein the upper computer is connected with the control panel through the wireless communication module, the control panel is electrically connected with the relay, and the relay is electrically connected with the electromagnet.
 6. A use method of the lower limb exoskeleton system having jump-down cushioning function according to claim 5, comprising the following steps: step 1: the lower limb exoskeleton system is worn to a lower half part of a human body of a wearer, the back frame of the lower limb exoskeleton system is fixed to a waist of the wearer through binding tapes and the waist binding frame, the telescopic thigh bars are fixed to thighs of the wearer through the upper leg binding frames and binding tapes, and the shank bars are fixed to shanks of the wearer through the lower leg binding frames and binding tapes; and step 2: when the wearer walks on flat ground, motors in the knee joint movement mechanisms output torque to control the walking action, and harmonic reducers of the knee joint movement mechanisms convert rotation of outer shafts of the motors into flexion and extension movements of the knee joint movement mechanisms, so that the hip joint movement mechanisms are driven to passively follow the wearer to move; when jump-down movement is needed, the upper computer sends instructions to the control panel via the wireless communication module, output pins of the control panel control the relay to be connected, the electromagnet is electrified to be connected to drag the traction ropes and open the clamps, and the cushioning spring compressed into the shell pushes the moving sleeve to a limit position under the action of spring force; in a landing process, the rubber mat is in contact with the ground and presses the moving sleeve into the shell under the action of ground support forces, so that the cushioning spring is compressed into the shell again; after complete landing, the upper computer sends instructions to control the control panel, and the output pins of the control panel control the relay to be disconnected so as to disconnect the electromagnet and loosen the traction ropes; and the clamps are pushed to clamp the moving sleeve under the action of the reset springs, and therefore, the cushioning spring is compressed in the shell without popping out to finish an entire jump-down cushioning action. 